Studies leading to the present invention were supported in part by funding from the Office of Naval Research, and the United States Government has rights in this invention as a result thereof.
1. Field of the Invention
This invention relates to compositions obtained from natural sources useful for the treatment of submerged surfaces, such as marine or other aquatic structures of ship hulls, in order to prevent fouling of the surfaces by aquatic organisms.
2. Background Information
It is well-known that the growth of organisms (micro- or macro-fouling matters) on the submerged parts of a structure may have detrimental effects on their operation and their corrosion rate. For example, in the techniques of oil production at sea, the fouling may accelerate the corrosion of submerged structures such as supports of drilling platforms. The weight increase resulting from the deposit of the fouling matter also results in difficulties when raising up certain submerged structures, as it is the case for the pipe-lines used to collect oil at sea; it also requires frequent operations for the maintenance of the floats of signal or meterologic buoys. On the other hand, the formation of even a very thin layer of microfouling is sufficient to reduce the transmission of light and sound and consequently to disturb the operation of certain devices such as sonar sea-marks. The fouling matter may also be a medium favorable to the proliferation of certain microorganisms responsible for the biodegradation of organic materials and of concrete. It is also known that the cooling systems for plants and power stations, either of the nuclear or of the conventional type, that are operated with sea water are also subject to severe fouling which may plug ducts and condensors. Finally, fouling by large organisms such as the balani, the serpulae and the algae, increases the roughness of the hull of ships and their drag in water, thereby resulting in an increase of fuel consumption and/or a reduction of the ship speed. These various problems and their consequences emphasize the importance of anti-fouling substances.
Besides the periodic cleaning of the surfaces or the use of paints enabling a controlled exfoliation, which are very expensive remedies, the principle of most anti-fouling action is to create a toxic zone on the surfaces to be protected. For example, chlorine is used successfully in a continuous manner in sea water ducts, but this technique is obviously unsatisfactory as far as the preservation of the natural environment is concerned.
An efficient way of combating fouling must (by prior art) comprise the maintenance of the toxic product at an efficient and homogeneous concentration and in a continuous manner on the whole surface. This is the reason why the so-called "anti-fouling" paints have taken an important place among the anti-fouling means. Thus, in order to fight against the growth of sea organisms on submerged surfaces and hulls of boats, an anti-fouling paint is generally applied as an upper layer. According to the known techniques, this antifouling paint contains a toxic substance which slowly reacts with sea-water to give a salt soluble in water and which is lixiviated from the paint pellicle. Among the toxic substances which are the most commonly used, there can be mentioned cuprous oxide, tin tri-n-butyl oxide, tin tri-n-butyl fluoride and tin tri-n-butyl sulfide, these compounds being biocidic agents with activity against a wide range of a sea organisms.
However, these organo-metallic compounds are general toxicants and have adverse effects on all types of sea life, their action not being limited to the inhibition of marine fouling. More specific anti-fouling compositions are therefore desirable. For example, it was known that various marine organisms apparently were resistant to fouling of various types. It was unlikely that a general toxicant was excreted by such marine organisms because of the abundance of marine life in the vicinity of such organisms, such as corals. However, isolation and identification of the active compounds in marine corals had not taken place prior to the present invention. Accordingly, there remained a need for substances of biological origin that exhibit less toxicity when used as antifouling agents than those materials that were previously used.